This invention relates to a method of franking postal items by which postal authorities are enabled to account for charges relating to the handling of mail items and to obtain payment for such charges from the sender of the mail items. The invention also relates to franking apparatus for carrying out the method.
Currently used postage payment systems for franking machines fall into two categories. In one category, in which the postage is prepaid, the franking machine is constructed and operated to securely maintain a record of credit remaining available to a user of the machine and the machine is controlled to lock if and when the credit level decreases to a predetermined low value. Consequently if this low credit level is reached and the machine locks, the machine is unable to be used for further franking until such time as payment has been received by the postal authority for additional credit and the new credit value has been entered in the machine. In the other category in which a post payment method is used, the meter is read periodically and the user invoiced accordingly, use of the franking machine is constrained by controls which lock the machine when total postage value used exceeds a predetermined limit. In both of these categories of system it is necessary for the franking machine to incorporate security measures to prevent fraudulent use of the machine. In order to maintain the integrity of the security complex control systems are used in the internal operation of the machine and the franking machine is constructed to be physically robust and is provided with sealing devices to prevent unauthorised access to the interior of the machine. In addition to the security maintained in the franking machine, the postal authorities operate an elaborate manual procedure for checking franked mail items which necessitates restriction of location at which franked mail can be posted by any sender. The maintenance of security in the franking machine increases the cost of the franking machine and this together with restrictive posting procedures tends to limit the use of franking machines to those users which have a relatively large volume of postal usage.